1. Field of the Invention
The present invention relates to improved nitramine-containing propellant fomrulations, and more particularly to a formulation which does not exhibit sharp exponent shift in the burning rate curve.
2. Description of the Prior Art
Nitramines are of interest for gun and rocket propellant applications because they are an energetic source of smokeless combustion products. There has been increasing activity involving propellant formulations containing nitramine compounds for use in guns. One reason for this is the need for increased muzzle velocity within acceptable pressure limits while retaining good barrel life. Nitramine containing formulations are also of interest in efforts directed toward developing lower vulnerability propellants.
However, considerable difficulty has been encountered in obtaining the ballistic performance expected on the basis of thermochemical properties. The newer nitramine propellants exhibit combustion anomalies which are referred to as pressure sensitivity factors. The problem has many aspects, but is best summarized in terms of burning rate curves, where nitramine propellants exhibit sharp "exponent break points" or exponent shifts in the logarithmic burning rate curves. This lack of a smooth burning and break point appearance with rapid burning has long been a problem in the formulation of nitramine propellants of all types. It has been observed that many of the formulations have burning rate vs pressure characteristics which are substantially different from those of the conventional nitrate ester gun propellants. Many of the compositions have pressure exponents &lt;1 below 4000 psi and &gt;1 above 4000 psi. The difficulties encountered in obtaining the desired ballistic performance with these propellants are usually attributed to the above-described pressure vs burning rate behavior.